Compile-time and runtime casting c#

Question

I was wondering why some casts in C# are checked at compile-time whereas in other cases the responsibility is dumped on CLR. Like above both are incorrect but handled in a d

Answer 1

If your variable is of Base type, is can be theoretically constructed by Derived constructor, thus being a variable of Derived type actually. At compile time, compiler does not bother itself with trying to figure out whether in each particular case such downcast (representing a variable of Base type as an entity of Derived type) is possible.

Your sample is simple - you create a new class and cast it right away. But what if you get Base from somewhere else, e.g., some method call? Compiler just cannot "guess" what your method is going to return and therefore throw on not throw an error.

When you cast Other, compiler sees that there is no possibility that Other is actually Derived and throws an exception.